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Friday, September 28, 2012

Unfortunately, my computer has stopped working. Updates in the blog will be suspended for likely at least the next few days. Brief updates on the forecast and on the status of the blog will be posted on the NYC Area Twitter page for now.

9/30/12 - A preview of the October outlook has been posted in the Long Range page. The full outlook will be posted at some point this week.

**Tuesday, 10/2 Update: Blog updates will resume tomorrow (Wednesday, 10/3). The October outlook will be posted as well.**

1. Today's storm was faster moving than expected but also produced less rain than my outlook called for last night, which was on the conservative side of the model guidance, with most places north and west of NYC seeing up to or a little over 1/2 inch. The most significant impact from today's storm, however, came in NYC, northern Long Island and coastal Connecticut, where a severe thunderstorm developed producing strong wind gusts and flash flooding, with radar estimates showing 2-4 inches of rain in coastal areas. More information on today's observations will be posted with tonight's update.

2. A forecast change has taken place for next week's outlook, as latest indications point to a low pressure affecting the region on Tuesday with widespread rain. This is only a recent change, and more information on the outlook for next week will be posted tonight, including an update on the long range cool spell and some thoughts going forward into October.

Tonight's update will discuss the aforementioned topics in more detail.

The latest radar, posted to the left, shows the rain that will affect the region tonight into tomorrow located over Pennsylvania. The storm appears to be ahead of schedule, and is expected to clear most of the area by noon except for eastern areas, which will see some showers persisting beyond noon. The heaviest rain is expected to stay north of the area, with showers and thunderstorms expected to affect the area with the peak during the morning hours. Rain totals are expected to end up between 1/2 and 1 inch, locally up to 2 inches, north and west of NYC, with lower totals for Long Island. Temperatures will warm up into the upper 60s to low 70s across the area.

As the wave of low pressure moves out, mostly cloudy skies will continue for the weekend with a risk of scattered showers, especially east and NE of NYC, as an upper level low remains in place over the region. Temperatures are expected to reach the mid 60s to 70 degrees on Saturday and the upper 60s to low 70s on Sunday. Similar temperatures are expected again for Monday.

Tuesday - Beyond: Warming Up

The upper level low will gradually exit the region, with another wave of low pressure expected to stay south of the area on Tuesday. More sustained ridging will then build into the region for the first time since mid September, with temperatures quickly warming up across the region well into the 70s, likely peaking in the mid to upper 70s in the area during the peak of the warm spell. Uncertainty increases for the longer range as models differ with their handling of a dropping cold air mass in Canada; although there is expected to be ridging in the western Canada/NE Pacific region, it appears that the trough will extend towards the southwest US, which at least through the medium range should prevent an amplified trough from dropping into the region, rather favoring more of a gradual cool down with temperatures likely returning towards the 60s-low 70s range. With the pattern uncertainty there are model differences regarding the timing of the next cold front, although it appears that it may come through sometime late next week or next weekend with the possibility of rain. Stay tuned for more information on the longer range.

The latest radar shows scattered showers across parts of New York and Pennsylvania. Scattered showers are possible throughout tonight and Thursday at times with mostly cloudy skies persisting; originally, Thursday was expected to clear out, although the front will fail to progress as far south as originally expected, instead slowing down and stalling over the region rather than dropping south and then retreating north. Temperatures on Thursday will reach the upper 60s to low 70s inland and the low to mid 70s across the rest of the area.

Friday - Monday: Cloudy, Chilly, Rainy

A weak wave of low pressure is expected to move through the region, producing a round of rain on Thursday night into the first half of Friday. There is still some uncertainty regarding exactly where the heavier rain axis sets up and how much rain falls, which will also influence the temperatures, although at this time there is a high probability of at least a steady moderate to locally heavy rain to focus from NYC and further north/west especially in the first half of Friday. If the currently modeled scenario verifies, high would end up in the mid to upper 50s north/west of NYC and in the low to mid 60s from NYC and further east. Some of the latest models are further north, however, with the latest NAM run taking almost all of the rain north of the area with highs in the upper 60s to low 70s. For tonight's forecast, I am siding with a scenario north of the model consensus, with highs potentially in the mid 60s inland and the upper 60s across the rest of the area. With the aforementioned uncertainty, the forecast is still subject to some changes. Stay tuned for more information on Friday's forecast with updates on Thursday.

It does not appear that a stronger organized area of low pressure will develop, although showers and clouds will persist across the region throughout the weekend, mostly focusing over New England but with scattered showers across the area, mainly east of NYC but extending west of NYC occasionally as well. Temperatures will be slightly warmer, in the mid to upper 60s on Saturday with more widespread upper 60s on Sunday, perhaps getting into the low 70s in the immediate NYC area. Additional showers are expected for Monday with highs similar to those of Sunday. More information will be posted on this time frame as details become clearer.

With the additional chilly temperatures expected, the possibility may be there that parts of the area could end up slightly below average for the month of September; since early 2011, the majority of the area failed to have any cooler than average months. More on this possibility will be posted over the next few days.

Longer Range: Warming Up

The persistent trough pattern that has been in place since 9/15 is expected to break down early next week, with a less amplified pattern returning as ridging temporarily rebuilds into the East. A surge of warmth is expected to move into the region with temperatures reaching the 70s across parts of the region, including NYC on Tuesday, and a larger part of the region on Wednesday. Afterwards, model differences emerge again, with the GFS quickly bringing a cold front followed by a strong cold air mass, while the ECM and CMC keep a warm pattern in place through next weekend. At this time, I am considering the 18z GFS scenario a likely outlier, with a strong cold pattern unlikely to return in the medium range. Stay tuned for more information on the longer range outlook.

An area of showers is currently approaching the region, and will provide some rain across the area tonight. Mainly cloudy skies are expected to continue for Wednesday and Wednesday night with scattered showers but with generally light totals up to 1/4 inch for most places. Highs are expected to warm into the mid to upper 70s from NYC and further north/west and the mid 70s east of NYC. Temperatures may reach 80 degrees in parts of the immediate NYC area. Partly cloudy skies are expected on Thursday with the risk of isolated showers and highs cooling down into the upper 60s to low 70s inland and the low 70s across the rest of the area.

Friday - Beyond: Some Rain, Chilly Temperatures Expected

The briefly drier conditions will only be short lasting as another rain event sets up for Friday into the weekend. A closed 500mb low will drift towards the region as a surface low pressure develops off the coast. An initial round of rain is expected on Friday, with mainly cloudy skies, occasional showers and highs only in the 60s across the area; at this time, I am keeping highs in the mid 60s, although this may need to be adjusted lower should the rainier scenario verify. Uncertainty then increases for the weekend as there is still uncertainty regarding the exact development of the low pressure; the latest GFS run goes back to showing the old scenario of a stronger low pressure developing and tracking north through the region, producing widespread rain, while the ECM, CMC and NAM show little additional rain. Although at least some rain is expected during the weekend regardless of which scenario verifies, the scenario first mentioned is still uncertain, and at this time my forecast maintains a chance of some rain for the weekend, although the outlook is still subject to change. Temperatures will remain chilly, generally in the mid 60s to low 70s, although should the rainier outcome verify temperatures would be colder. Stay tuned for more information on the weekend outlook.

Following the cool air mass that resulted in widespread highs in the mid to upper 60s across the area today, cooler lows are expected tonight with less cloud cover, dropping into the upper 30s inland, low to mid 40s in interior parts of NE NJ, SE NY and southern CT and typically cooler parts of eastern Long Island, mid to upper 40s in the closer suburbs of NYC, and low to mid 50s in NYC. Areas of frost may be possible for interior areas; should this verify, it would be the first frost of the fall for the area. Mostly sunny skies are expected for Tuesday with highs reaching the low to mid 70s across the area.

An approaching cold front will bring increased cloud cover overnight with some showers expected for Wednesday and Wednesday night. Highs are expected to reach the low to mid 70s across most of the area with mid to upper 70s in the immediate NYC area. Overnight lows will be in the 50s for most of the area with 60s in NYC and its surrounding suburbs as cloud cover and scattered showers persist.

Thursday - Next Weekend: Chilly; Dry Start, Potentially Wet Ending

Behind the cold front, another trough will enter the region, although in this case as a more progressive pattern returns with less western Canada and western Atlantic ridging, the trough will be flatter and less amplified than the previous troughs, failing to drop much into the region while the cold front stalls near the central Mid Atlantic, keeping at least partly sunny skies in the forecast for Thursday and Friday. Highs will reach the mid to upper 60s across most of the area with some low 70s on Thursday, slightly warming up on Friday, with overnight lows likely to drop into the low to mid 40s inland and the mid 40s to 50 degrees across the rest of the area with low to mid 50s in NYC.

Uncertainty increases for the weekends as a closed 500mb low moves towards the region but with each model showing a different outcome. Some of today's model runs initially showed a coastal low pressure developing offshore and moving north into the region, providing widespread rain, although have since backed down from that scenario. The general outlook for this time period has a somewhat higher confidence level, with at least some showers expected around Saturday and/or Sunday, with temperatures staying chilly, generally in the 60s to low 70s. The expected set up is more uncertain, however, and at this time there are too many differences to make a high confidence call. Stay tuned for more information on the weekend set up.

Monday, September 24, 2012

Sunday, September 23, 2012

- Chilly temps to return again; highs in 60s, lows in 40s- Interior areas to possibly drop below 40 degrees for lows- Brief warm up towards Wednesday with some rai - Another cool down for the late week

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Sunday - Tuesday: Chilly Temperatures Return

Another strong cool air mass will move into the region behind the cold front currently moving through the region. Highs on Sunday will only reach the upper 60s to low 70s across the area with mid 60s for interior areas. Overnight lows are a bit more tricky with a shortwave moving through on Sunday night into the first half of Monday with increased cloud cover especially from NYC and further north/west. Due to the increased cloud cover, I went slightly warmer than modeled for Sunday night lows, dropping into the low 40s inland, mid 40s to low 50s in the north/west suburbs of NYC, and the low to mid 50s in NYC. Eastern areas are expected to cool down more prior to the arrival of the shortwave, with temps likely dropping into the low 40s in the coolest areas in eastern Long Island and parts of southern CT, perhaps dropping slightly below 40 degrees in the cooler scenario. Monday night is expected to be the coldest night with mainly clear skies, with temperatures dropping into the mid to upper 30s inland and the low to mid 40s for most other places, with the exceptions including upper 40s in the closer suburbs of NYC and low to possibly mid 50s in NYC. The coolest daytime highs will be on Monday, peaking in the low to mid 60s inland and the mid to upper 60s across the rest of the area, with slightly warmer temperatures expected for Tuesday in the upper 60s to low 70s.

Wednesday - Beyond: Briefly Warmer, Then Chilly

The next cold front will move through the region late on Wednesday, with additional showers and possibly thunderstorms expected. A brief warm up is expected with highs reaching the low to mid 70s across the area. Behind the cold front, another trough will move into the region for Thursday into the weekend, with highs again returning into the 60s to low 70s and lows in the 40s outside of the immediate NYC area. By this time period, however, the pattern will be less amplified than it is now and slightly more progressive following the departure of the strong ridging east of Atlantic Canada. There is more uncertainty going into next weekend and beyond although the latest model guidance suggests the possibility for another rain event next weekend.

Saturday, September 22, 2012

- Scattered storms, some strong, Saturday evening N/W of NYC- Another cool down for Sun-Tues; highs in 60s, lows in 40s- Rain event possible mid-late next week- Chilly pattern continues through end of month
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Saturday - Tuesday: Storms, Then Chilly Again

The next cold front will move through the region on Saturday evening through the overnight hours as a strong trough drops into the north central US, bringing another surge of colder than average temperatures into the north central and NE US with a trough locked over the region as a result of the current pattern. Temperatures on Saturday are expected to warm up into the mid to upper 70s across the area, with parts of the immediate NYC area reaching and/or slightly exceeding 80 degrees. Marginal instability and shear are expected, although unlike Tuesday's cold front, there is no strong low level jet present in this set up, and mid level lapse rates are unfavorable as well. The timing of the day is also less supportive with the storms mostly moving into the area towards the evening and early overnight hours. Scattered thunderstorms are expected, especially north/west of NYC, with some of these storms strong with gusty winds the main risk, although no widespread severe weather outbreak is expected. Dry conditions will return by early Sunday morning.

Winter weather is associated with the strong trough entering the north central US; snow has been reported tonight in Minnesota, including Duluth, with some snow expected in the Great Lakes region on Saturday and possibly even in the high elevations of the Northeast on Monday. The cool air mass will spread into the Northeast, with 850mb temperatures expected to drop to near 2-4 degrees Celsius, the coldest observed so far.

Temperatures on Sunday will peak in the upper 60s to lower 70s across the area with mostly sunny skies. The coldest temperatures are expected for Sunday and Monday nights; with mainly clear skies, temperatures will drop into the upper 30s to low 40s for interior areas and the mid to upper 40s across the rest of the area except for NYC, in the low 50s. The coolest high temperatures are expected for Monday with highs only in the low to mid 60s inland and the mid to locally upper 60s across the rest of the area, with Tuesday's temperatures slightly warming into the upper 60s to lower 70s across most of the area.

Wednesday - Beyond: More Showers, Then Colder Again

A pattern change that unfolded early this week sent the US into a warm west and chilly central/east pattern, with persistent ridging near the western US/western Canada and near the Davis Strait and east of Atlantic Canada keeping a trough locked over the central US and parts of the NE US. The pattern is expected to generally continue through the rest of the month, with additional cool spells expected. The next cold front to move through the region will be on Wednesday with additional showers likely. Cooler temperatures will return for Thursday through Saturday with highs likely returning into the mid 60s to low 70s range along with lows again in the 40s for most of the area away from NYC. While temperatures are likely to warm up into early next week, at this time there does not appear to be any significant warm spell on the way.

Friday, September 21, 2012

A more detailed discussion of the forecast and a review of Tuesday's wind/rain event will be completed and posted tonight.

Forecast Overview:

Today - Saturday: Following a slight warm up in temperatures today into the 70s, the peak of this brief warm surge will take place on Saturday with highs approaching 80 degrees in the immediate NYC area. A cold front will move through at night with scattered thunderstorms, especially north/west of NYC. The storms could be locally heavy with some strong storms possible, with gusty winds the main risk, although no widespread severe weather outbreak is expected.

Behind the cold front, the coolest temperatures of the fall so far will come in with another strong trough, as the current pattern favors a colder pattern for the eastern half of the US. Overnight lows will drop into the 40s for most of the area except for NYC on Monday and Tuesday nights, with high temperatures the coolest on Monday, only peaking in the mid to upper 60s across most of the area, slightly cooler for interior areas.

Temperatures will briefly warm up again towards the middle of next week, returning into the 70s ahead of the next cold front moving through around Thursday. Colder than average temperatures are likely to return again behind the cold front by Friday and next weekend with highs likely staying below 70 degrees again.

Today - Tuesday Night: Dry, Then Stormy
Mostly to partly sunny skies will continue today, with increasing clouds overnight as showers and thunderstorms spread in from the southwest as a strong cold front approaches. Two rounds of thunderstorms are expected; the first will be in the morning to early afternoon hours, likely starting around 5-7 AM and lasting through at least 12-2 PM, when heavy thunderstorms are likely, possibly strong. The main risk with these thunderstorms will be strong wind gusts, and an isolated tornado potential cannot be ruled out. A brief break in the storms, especially east of NYC, is expected around the mid to late afternoon hours, although scattered strong thunderstorms are still possible, especially north/west of NYC. During the afternoon and late afternoon hours, winds will increase with gusts in the 40-50 mph range expected, likely exceeding 50 mph towards eastern areas.

The line now appears to come through earlier than originally expected, likely moving in after 9-11 PM into NYC. Some thunderstorms along the line will be severe, with strong wind gusts the main risk from the line. Heavy rain is also expected with localized flash flooding possible north/west of NYC. The storms will continue to move east through the area overnight, with drier conditions by Wednesday morning.

Wednesday - Beyond: Cooling DownHighs on Wednesday will reach the upper 60s to lower 70s across the area with clearing skies, with overnight lows dropping into the low to mid 40s inland, upper 40s to mid 50s for the north/west suburbs of NYC and southern CT, and the mid to upper 50s in NYC. The cold front will fail to progress much east of the region, and as a result, temperatures will fail to significantly cool down. Thursday's temperatures will be similar to those of Wednesday, with slightly warmer lows on Thursday night. Widespread highs in the low to mid 70s will return by Friday.

The next cold front will likely move through around late Saturday into Sunday as another strong trough drops into the north central US. Not much precipitation is expected with this trough as less moisture from the Gulf of Mexico is expected compared to tomorrow's cold front, with cooler temperatures returning behind the front. The surge of cooler temperatures is also expected to remain transient, quickly moving out afterwards, but with ridging in Canada further east than the current observations, this cool period late next weekend into early next week may result in colder temperatures compared to those expected for later this week.

Note: The post date is from Sunday, 9/16 since it was posted after midnight. This post belongs to Saturday, 9/15's night update. Sunday's update will be posted on Sunday night.

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Observations for Saturday, September 15 have not been posted yet.

Tonight - Monday: Dry; Chilly Start, Then Warmer
A trough remains in place over the region behind last night's cold front, with a high pressure in place and 850mb temperatures near 4-7C, resulting in chilly temperatures for the region. Mostly clear skies will continue tonight with lows dropping into the low to mid 40s inland and the upper 40s to low 50s for the rest of the area except for NYC, in the mid to upper 50s. Mostly sunny skies will continue through Sunday with highs in the low to mid 70s across the area. Overnight lows will be similar to those of tonight, although slightly warmer, with highs on Monday warming up into the mid to upper 70s as a warmer air mass spreads in and 850mb temperatures warm up to near 10C.

Monday Night - Wednesday: Storm Produces Strong Storms, Heavy Rain

The next significant weather event to affect the region will take place on Tuesday into Wednesday. A pattern change is currently unfolding which will be discussed in more details in the next section, as the North American pattern becomes more amplified with ridging developing over the western US and Alaska as well as near Atlantic Canada. A trough will drop into the central US, moving towards the region with moisture drawn from the Gulf of Mexico up the East Coast ahead of a strong cold front. There is some uncertainty with the exact scenario, although it appears at this time that there will be two main rounds of storms. A round of scattered storms, locally heavy, is likely around Tuesday morning, mainly before 12-2 PM. Following these storms, drier conditions are likely for the late afternoon into the early overnight hours with the heaviest rain staying to the west of the area, although scattered showers/storms may still be possible especially north/west of NYC. Temperatures will peak in the mid 70s across most of the area.

The cold front will approach overnight, moving through on Wednesday morning, with temperatures barely dropping or remaining steady overnight in the upper 60s to low 70s across most of the area. While not much instability is expected, favorable wind shear and a strong low level jet will result in the potential for strong/low-end severe thunderstorms with the cold front overnight, especially after 2-4 AM, with strong wind gusts the main risk. Windy conditions are also likely prior to the arrival of the main storm line. With precipitable water values approaching 2 inches, the potential is there for heavy rainfall locally above 1-2 inches with the cold front. Widespread severe weather to the extent of last Saturday (9/8) is not expected. Storms are expected to persist into Wednesday morning, especially from NYC and further east, with clearing skies later into the day with highs generally in the low to mid 70s. Stay tuned for more information for Tuesday and Tuesday night's outlook.

Thursday - Longer Range: Pattern Change Expected

As previously mentioned, a pattern change will take place starting from the middle of this week. An increasingly amplified pattern will develop with more ridging towards the western US and Alaska as well as Atlantic Canada and the Davis Strait, which will result in a more persistent trough pattern in between, with the trough axis near the central US, where below average temperatures are expected along with frequent troughs. The 12z ECMWF, posted to the left for Friday, 9/21 from the Pennsylvania State University e-Wall, shows the pattern expected with the ridging near Atlantic Canada and the western US with a strong trough in between. As the trough axis will remain over the central US, temperatures are likely to average out to generally close to average for the area through the end of the month, with occasional transient cool spells but with the core of the cold staying west/NW. This pattern favors near-above average precipitation mostly focusing towards the eastern half of the US. This pattern is remarkably different than that observed during last year's fall, when the pattern was much more progressive with less amplitude, with a lack of sustained troughs in the US and persistent ridging near the western US and Greenland.

Temperatures will briefly cool down following Wednesday morning's cold front, with cooler temperatures returning for Wednesday night and Thursday. With a SW flow still in place and the cold front failing to progress much to the east of the region, the cool air mass will lift back into Canada as a warmer air mass spreads in again with temperatures warming up by the late week into next weekend. Uncertainty increases by next weekend with another storm potential which each model handles differently, although the potential is there again for rain towards late next weekend or early next week. Stay tuned for more information on the longer range.

Saturday, September 15, 2012

Tonight - Monday: As of 1 AM Saturday, a line of light to locally moderate showers is moving east through NE PA. Isolated showers are expected into early Saturday with clearing skies later into the day. Highs will reach the low to mid 70s across the area.

Mainly clear skies will continue through Monday with a trough in place along with a high pressure. Chilly temperatures will briefly return, with lows dropping into the upper 40s to mid 50s away from NYC for Saturday and Sunday nights with mid 40s for interior areas and mid to upper 50s in NYC. Highs will meanwhile reach the lower to mid 70s on Sunday, perhaps slightly below 70 degrees inland, warming up with more widespread mid 70s on Monday.

Tuesday - Early Wednesday: Rain, Strong/Severe Storms
A developing low pressure will move from the Ohio Valley into Canada, bringing a widespread moderate-heavy rain event for the East Coast along with a potential for strong to severe storms. Most of the rain and thunderstorms are expected to take place towards the second half of Tuesday into the overnight hours; mainly cloudy skies and occasional storms could be a limiting factor for severe weather chances, although shear is modeled to be favorable for severe weather, with high precipitable water values near 2 inches resulting in the potential for heavy rain with the storms. Saturday's update will discuss the thunderstorm potential in more detail.

Beyond: Colder Central US, Transient Cold Eastern US
A pattern change is expected for the medium range as the pattern becomes noticeably more amplified, with the development of stronger and more persistent ridging into the western US and Alaska along with some ridging near Greenland while a strong trough drops into the central US. The main trough axis will remain over the central US where the coldest temperatures are expected; the cool temperatures will be more transient over the eastern US including the area, resulting in additional storm chances and a higher probability of near-above average precipitation for the medium range. Temperatures are likely to end up generally close to average as a whole, accounting for transient cool spells and warmth surges, with above average temperatures towards New England and below average temperatures into the central US.

Forecast Overview:Tonight - Friday: Mild temperatures will return again tomorrow, although the warm spell ended up slightly less warm than expected, which will be discussed in more details tomorrow. High temperatures on Friday will be similar to those of today, in the upper 70s to low 80s.

Saturday - Monday: A mainly dry cold front will come through late on Friday night with isolated showers/storms expected, followed by clearing skies on Saturday with highs in the low to mid 70s across the area. Overnight lows will drop into the mid to upper 40s for interior areas with mainly clear skies and the low to mid 50s for the rest of the area except for NYC, with lows in the mid to upper 50s. Highs on Sunday will be at least 1-2 degrees colder than Saturday's highs, with overnight lows slightly warmer than those of Saturday night. Clouds will increase on Monday with highs in the low to mid 70s across the area.

Monday Night - Beyond: A widespread rain event is expected for Tuesday into early Wednesday. Rain will develop in the overnight hours on Monday, lasting occasionally throughout the day on Tuesday and Tuesday night with highs likely again in the low to mid 70s for most of the area. Rain will continue into the overnight hours before ending early on Wednesday, with less cloud cover later into Wednesday along with similar temperatures. A cooler air mass will briefly move in with slightly cooler temperatures into Thursday, but the trough axis will remain over the central US, with any prolonged stretch of dry and cool weather failing to move into the region as temperatures are likely to generally stay in the 70s.

Tonight - Friday: Chilly, Then Warming UpFollowing the chilly temperatures observed this morning, chilly temperatures are expected again for tonight but not as cold as those of last night, with temperatures dropping down into the mid 40s inland and the upper 40s to mid 50s for the rest of the area except for NYC, likely in the mid to upper 50s.

Mainly sunny skies are expected for Wednesday through Friday with highs warming up, reaching the upper 70s to low 80s across most of the area. Similar temperatures are expected through Thursday and Friday, with overnight lows gradually warming up with each night.

Next Weekend - Early Next Week: Some Rain

**Wednesday, 9/12 Noon Update: An unexpected change took place in the forecast which invalidates the previous outlook for Friday night through Tuesday. The original outlook called for a closed low to drift through the Northeast during the weekend with more clouds and scattered showers along with slightly cooler temperatures; this was supported by the entire model guidance with decent consistency. The trough dropping into the US was modeled to be more detached from the main flow, dropping into the north central US and then drifting east into the NE US. Instead, the entire 0z model guidance last night significantly altered that scenario, and instead, the trough is expected to remain progressive and quickly move out, which results in a dry and quick moving cold front on Friday night into Saturday with more cloud cover and perhaps a few sprinkles, followed by a short lasting surge of cooler temperatures on Sunday, slightly warming up early next week. More information will be posted on this with tonight's update.

Mid Next Week - Beyond: Cooler Pattern Develops
By the middle of next week, trends are pointing to a pattern change with increased amplification as stronger and more persistent ridging develops near Alaska and the western US. Having ridging in these areas is key to getting a colder pattern in the central/eastern US, and was almost entirely missing from last year's warm winter pattern. Teleconnection outlooks point to a positive PNA, a falling NAO although without a strong -NAO due to the absence of strong ridging near Greenland, and a negative EPO; during last year's season, the EPO was dominantly positive and was a contributing factor to the warm pattern. With the changes above, a pattern consisting of more troughs may develop for the central US with colder than average temperatures. Some of the cooler temperatures may occasionally spread into the eastern US, although the main trough axis appears to remain near the north central US, with temperatures potentially ending up near to slightly above average for the eastern US, below average at times, along with near-above average precipitation for the second half of the month; the time period around mid to possibly late next week has a stormier look for the eastern half of the US. Temperatures overall for September are still expected to end up at least slightly above average, continuing the unprecedented stretch of 18 months of consecutive warmer than average months for many places, but should end up not far from average as opposed to significantly warmer than average.

Storm updates are done for tonight. The next update will be posted on Sunday with a summary of today's storm activity as well as an updated forecast for the area.

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5:31 PM: A Tornado Warning is in effect for NW Bergen County into SE Rockland County associated with a severe storm. The storm is capable of producing strong wind gusts along with heavy rainfall.

4:20 PM: Line Ahead of ScheduleThe severe squall line is already ahead of schedule, and is entering NW NJ. Severe storms are quickly developing just ahead of the line, and the line is expected to persist into northern NJ and SE NY, the area I highlighted for the biggest impact from the squall line. The line collapsed in SE PA and southern New Jersey, and may weaken extending further north as far north as NYC, although the severe storms are still expected to focus over NW/north central NJ and SE NY over the next 2 hours, ending by 7 PM. The biggest risk from the line is strong/damaging wind gusts, with small hail and heavy rainfall additional risks.

3:25 PM: Squall Line Approaching

Since the last update, additional scattered severe storms developed over NE NJ, with a tornado warned storm over NE Bergen and SE Rockland counties. The storms have moved to the north of the area, although attention now turns to the squall line over central/eastern PA, which is intensifying while moving east towards the area. The line is ahead of schedule, currently located further east than modeled, and is expected to move into northern NJ, SE NY and NYC between 5-7 PM. The biggest risk with this line is strong/damaging wind gusts, along with small hail, heavy rainfall, and the additional possibility of isolated tornadoes.

12:15 PM: More Severe Storms TodayAn unexpected morning round of severe thunderstorms developed over the immediate NYC area, which resulted in two tornado warned storms, one in Brooklyn and the other in Rockland and Westchester counties. The most significant storm was over Queens, specifically in Breezy Point, where there are many reports and videos of a tornado touchdown as well as reports of damage and flash flooding. More updates on this will be posted as new information comes in.

Although the morning round was unexpected, more severe thunderstorms are expected today. Isolated storms are expected through the rest of the afternoon, with some of these storms also capable of becoming severe with strong winds, flash flooding and isolated tornadoes. The main event is expected to be tonight with a strong squall line which is currently near western Pennsylvania. This line is expected to contain strong to severe storms as it moves east into New Jersey later tonight, towards 6-8 PM. The strongest storms with this line are expected to stay north/west of NYC, especially from northern NJ into the Hudson Valley. The latest model guidance, however, shows weakening in the line once it reaches NYC, with some models entirely collapsing the line once it passes NYC and SW CT. More information will be posted on the evening outlook later today.

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12:22 PM:Tornado Warning remains in effect for Stamford to Danbury, CT. Strong storms are rapidly firing up over NE NJ, no tornado warned storms yet but flash flooding is possible with the storms training just east of the Garden State Parkway.

11:31 AM:Another Tornado Warningis in effect for parts of Rockland and NW Westchester counties in NY. The storm is located near northern Rockland county, moving to the NE.

There are reports of a tornado touchdown from the earlier tornado warned storm near Breezy Point in NYC. Multiple images posted online show a tornado, along with reports of damage in that area.

10:46 AM:A Tornado Warning is in effect for Brooklyn, NY. The severe cell is moving NNE into Queens, later on into far SW CT.

Forecast Highlights:- Severe storms likely tomorrow evening, especially north/west of NYC- Cooler temperatures expected for early next week- Gradual warm up late next week, highs rise back into 80s
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Weather News: A 71 year old man was struck by lightning from an isolated thunderstorm cell in Demarest, NJ, and was pronounced dead several hours afterwards. The storm popped up over NE NJ during the afternoon, with radar estimates showing localized totals near 1-2 inches in far northern areas.

Saturday's Outlook: Severe Storms LikelyA strong cold front will move through the region during the evening and early overnight hours on Saturday, bringing a widespread severe thunderstorm outbreak as well as pushing the moist and warm air mass out of the region. Partly cloudy skies are expected with increasing instability by the late afternoon and evening with high temperatures generally reaching the upper 70s to low 80s, perhaps the mid 80s in the immediate NYC area. The trough and cold front will become negatively tilted by the evening and night as a low pressure develops near western New York state and deepens while moving into Canada. Favorable shear parameters are expected, with surface-500mb bulk shear up to 50 knots according to the NAM.

With the favorable severe weather parameters, a squall line containing strong to severe thunderstorms is expected to develop to the west during the afternoon hours, moving through the area in the evening and early overnight hours, especially after 6-8 PM through 12-2 AM. The best dynamics and the highest risk of severe weather are expected from northern New Jersey through the Hudson Valley and western Massachusetts/Connecticut, where the potential exists for hail, strong/damaging wind gusts, and the possibility of isolated tornadoes. The combination of less favorable parameters and instability as well as the marine layer will reduce the severe weather potential for coastal parts of New Jersey and Long Island, as well as parts of southern/eastern Connecticut.

Stay tuned for more information on the severe weather outbreak with several updates on Saturday.

Next Week: Chilly, Then Warm
Behind the cold front, a fall-like air mass will enter the region from Canada, with 850mb temperatures dropping down to at least 6C, bringing the coolest temperatures since the spring. Mostly sunny skies are expected from Sunday through most of next week with a high pressure dominating the pattern over the Northeast region, with highs reaching the mid to upper 70s across most of the area, possibly peaking in the low 70s in interior areas. Widespread lows in the 50s are expected overnight with low 60s in NYC and upper 40s inland.

The coolest temperatures are expected for Monday and Tuesday, with highs in the low to mid 70s across the area. Monday night will have the coolest temperatures with mainly clear skies and light winds, with lows dropping into the 40s across most places outside of NYC. Temperatures in the suburbs of NYC are expected to reach the upper 40s to low 50s, with low to mid 50s in NYC. Temperatures inland are expected to drop into the low to mid 40s.

By the mid-late week, the high pressure will shift south of the area with a WSW flow developing, resulting in a surge of warmth into the region. Temperatures will gradually warm up, reaching the low to mid 80s by the late week and the upper 80s in parts of the immediate NYC area. There is more uncertainty for the longer range although the potential is still there for a cool down around early next week.

Tonight - Saturday Night: Warm, Then Stormy
Following today's cloudier than expected conditions which also resulted in temperatures busting on the low side, generally dry conditions are expected again on Friday along with partly cloudy skies. Temperatures will end up warmer than they did today, reaching the mid to upper 80s from NYC and further north/west and the low to mid 80s in most of Long Island and southern Connecticut. It is not out of the question that more cloud cover once again takes place and temperatures end up slightly lower than currently expected.

A strong cold front will move into the region on Saturday, with a relatively strong trough behind it. The cold front, which will also help to keep hurricane Leslie far away from the eastern US, is expected to move through late on Saturday night, with a strong line of heavy and strong/severe thunderstorms expected on Saturday evening and the first half of the overnight hours. This line will be capable of producing scattered to potentially widespread severe thunderstorms due to supportive instability along with favorable wind shear for severe weather. More information on Saturday evening and early night's heavy rain and severe thunderstorms will be posted with Friday's update.

Sunday - Next Week: Much Cooler, Then Warming Up
Behind the cold front, a large trough will move into the region, bringing a much cooler air mass behind it with 850mb temperatures dropping to at least 6 degrees Celsius. This will support the coolest temperatures since the spring, and the start of the transition to an autumn pattern. With a high pressure moving through the region, clearing skies are expected for Sunday with mainly sunny conditions for the first half of next week, while breezy NW winds are expected on Sunday. Highs on Sunday are expected to only reach the mid to upper 70s across most of the area with low 70s inland (interior north/west areas), with temperatures overnight dropping into the 50s for most places outside of NYC, with upper 40s possible inland and low 60s in NYC.

The coolest temperatures are expected for Monday and Tuesday with the coolest air mass overhead. High temperatures on both days are expected to reach the upper 60s to mid 70s across the area, with the coolest temperatures further inland and the warmest temperatures in the immediate NYC area. The coolest low temperatures are expected for Monday night with clear skies, light winds and chilly 850mb temps supporting widespread lows in the 40s over northern NJ, SE NY, southern Connecticut, and the typically cooler areas in central/eastern Long Island. Temperatures in the suburbs are likely to end up in the upper 40s to mid 50s, with mid to upper 50s possible in NYC. Temperatures are likely to drop into at least the low to mid 40s for interior areas.

Following the cool temperatures early in the week, the high pressure will slide south of the area with ridging building back into the region. As a result, temperatures will gradually warm up during the mid to late week along with dry conditions and mostly sunny skies, with highs likely reaching the lower to mid 80s across most of the area by the late week, possibly reaching the upper 80s in the immediate NYC area in the warmer case scenario. The longer range becomes more uncertain, although the possibility is there for another cool down towards the start of the following week. Stay tuned for more information on the cool early-mid week temperatures and the longer range outlook.

The forecast originally called for a widespread heavy rain event with widespread 1-2+ inches of rain, which was still conservative compared to other models supporting a more widespread axis of 3+ inches of rain. While amounts have already exceeded 1-2 inches locally, especially in central Long Island, parts of southern CT, and most notably in southern NJ where several inches of rain were observed this morning, widespread 1-2+ inches are no longer expected across the region from the rain event, which as the latest radar posted to the left shows is not enough to support widespread heavy region-wide rainfall.

The latest forecast is for additional scattered storms especially north/west of NYC tonight, some of them locally heavy/strong, with additional scattered storms during the day on Wednesday. Additional rain totals generally between 1/4 and 1/2 inch are expected, locally higher/lower.

As the remnant moisture from Isaac moves out, much warmer temperatures will briefly return for Thursday and Friday, with widespread highs in the mid to upper 80s expected from NYC and further north/west, perhaps reaching 90 degrees in parts of the immediate NYC area, with slightly cooler temperatures further east due to onshore winds. Humid conditions are expected to continue, resulting in slightly higher heat index values. There is a risk of isolated storms on both days, especially on Friday.

Weekend - Next Week: Rain, Then Perhaps Much Cooler
A relatively strong trough and cold front for this time of the year will move through the region on Saturday into Saturday night, producing widespread showers and thunderstorms. While there is still uncertainty with the exact timing and location, the potential is there for severe weather associated with the cold front. With the strong cold front moving through the region, Tropical Storm Leslie, which will likely be a hurricane by that time, will be kept offshore, while potentially strengthening into a major extratropical cyclone as it strikes Atlantic Canada. There is still some uncertainty with exactly how this setup plays out, regarding the cold front and how Leslie interacts with the trough, although there is an increasing likelihood of a relatively strong cool air mass dropping into the region, bringing a few days of much cooler temperatures. Should the aforementioned scenario with Leslie and the cold front verify, which is gaining model support, high temperatures would drop into the 70s and perhaps even some 60s along with sunshine, along with more widespread overnight lows in the 40s possible. Stay tuned for more information on the weekend and early next week outlook.

Monday, September 3, 2012

Due to difficulties with internet connection, no update was posted tonight. Twitter updates will occasionally be posted on Tuesday regarding the localized heavy rain for the next 2 days associated with Isaac's remnants.

Another hot day was observed across the area as the cold front moved through, although the model guidance suppressed the warm air mass more than actually observed, resulting in noticeably warmer than expected temperatures. Highs reached the mid to upper 80s across most of the area with lower 90s in most of northern NJ and the immediate NYC area. The hottest temperature was 92 degrees, tied with Teterboro, Newark and JFK.

Sunday, September 2 Observations:

Following the heat surge on Friday and Saturday, cooler temperatures returned as the warm air mass weakened and cloud cover from the remnants of hurricane Isaac spread into the region. Mostly cloudy skies were generally observed with isolated showers and thunderstorms, notably at night from Westchester into Rockland and Bergen counties, where a slow moving storm cell dumped locally near/over 2 inches of rain.

High temperatures were in the upper 70s to lower 80s across the area. The warmest high was 85 degrees in Montgomery, NY.

Week Ahead: Cloudy, Rainy, Cooler
Isaac's remnants slowly drifted through the central US over the last few days, producing widespread flooding along with severe weather and some tornadoes. While Isaac's remnants will no longer produce severe weather outbreaks when reaching the region, Isaac's remnants will deliver widespread moisture into the region with precipitable water values above 2 inches, resulting in a heavy rain potential this week.

A wave of low pressure associated with the remnant of Isaac will move through the region on Tuesday and Wednesday, producing a round of heavy rain. For Monday, mainly cloudy skies are expected with a few breaks in the cloud cover along with scattered showers/storms. More widespread storms are expected late on on Monday night into Thursday and the first half of Wednesday, when heavy thunderstorms are expected, especially during Tuesday night. Widespread rain totals above 1-2 inches are expected, perhaps getting as high as locally 3-5 inches in a few spots. Flash flooding is a concern with the heavy rainfall associated with Isaac's remnants. Cooler temperatures are expected due to the cloud cover and rain, generally in the mid to upper 70s in Long Island/S CT and upper 70s-low 80s for NYC and north/west, slightly cooler on Tuesday.

Less storms are expected for Thursday with the wave of low pressure moving out, although another cold front will approach the region afterwards. There is more uncertainty with this time frame, as a cold front is expected to move through around Friday, with a much drier frontal passage compared to the mid week storms associated with Isaac, although a trough is then expected to drop into the central US, likely to split from the main flow but with the location still uncertain. The ECM forms a cutoff low over the western Ohio Valley, while the GFS does so over the region. Drier conditions are likely for Friday through Sunday, with a risk of scattered showers/storms but with widespread rain unlikely at this time, with temperatures generally likely to end up in the upper 70s to low 80s for most places. Stay tuned for more information on the heavy rain this week and the potential rain early next week.